An electrical steel sheet is produced through processes of hot rolling a slab, annealing, if required, the hot rolled steel band for improving magnetic properties, pickling, cold rolling and finish annealing. It is known that this kind of steel is inferior in de-scaling properties during pickling, depending upon Si content as an essential element. There have been proposals for improving the de-scaling properties, e.g., in Japanese Patent Laid-Open Nos. 76,422/79, 33,436/81 or 138,014/85.
However with respect to the pickling of the hot rolled band, a big problem is involved about interglanular corrosions, irrespective of the de-scaling. If the electrical steel band is coiled at high temperatures after the hot rolling, the steel surface is effected with interglanular oxidation. If the pickling is continued unnecessarily after completion of the de-scaling, the corrosion grows as pitting in preference around the grain boundaries by the interglanular oxidation, and this fine cracks during a subsequent cold rolling, and deteriorates surface properties after the cold rolling. The fine cracks make various problems which not only degrade product values because of outer appearances of the products, but also deteriorate the magnetic properties, especially iron losses, by generating fine grains in the surface layers during finish annealing, and further cause of nonuniformity of insulation coatings.
Each of the above conventional proposals deals with the de-scaling only as the problem, and none of them specifies the pickling conditions by taking the intergranular corrosion into consideration.